This invention relates to a liquid heating apparatus, such as a boiler, utilizing an ascendant/descendant flowing system of a combustion gas.
The liquid heating apparatus as described above includes for instance, that which this applicant proposed in Japanese Utility Model Publication No. 15168/1956, is as shown in FIGS. 1 and 2. In this apparatus, an internal drum 22 comprising a dual wall is arranged in and at a space from an external drum 21 comprising a dual wall, with a combustion gas descending chamber 23 provided therebetween. An outer water chamber 26 having a hot water outlet port 24 and a water inlet port 25 in the upper and lower sections thereof respectively is provided outside this combustion gas descending chamber 23. An inner water chamber 27 communicated to the outer water chamber 26 with the upper and lower communicating tubes 28 is provided inside the combustion gas descending chamber 23. A combustion chamber 29 communicated to the combustion gas descending chamber 23 in the upper section thereof is provided in the internal drum 22. An exhaust port 30 is provided under the combustion gas descending chamber 23, a flue 33 is communicated to this exhaust port 30. A combustor 32 is detachably mounted through the inner and outer water chambers 26 and 27. It should be noted that the numeral 34 indicates a clearing port. In the liquid heating apparatus as described above, the combustion gas successively heated by the combustor 32 rises upwardly through the combustion chamber 29, the radiant heat being absorbed therein, and then the combustion gas is inverted in the upper section thereof such that the gas flows down through the combustion gas descending chamber 23 at a flow velocity g (m/sec). The flow velocity is increased to a velocity G (m/sec) at the exhaust port 30, and is exhausted to the flue 33. During this process, the combustion gas rapidly raises the temperature of the liquid by delivering the heat through radiation or contact to the liquid in the inner and outer water chambers 26 and 27 and raising the heat exchange rate between the combustion gas and the liquid. At the same time the descending fluidity is raised and the combustion efficiency is improved, so that incomplete combustion is advantageously prevented.
Although the conventional type of liquid heating apparatus provides the advantage as described above, it has the following problem. Namely, this liquid heating apparatus is as described above, and a flow path for a combustion gas in the combustion gas descending chamber 23 is narrow so that delivery of heat is efficiently carried out through contact by the combustion gas. In other words;
(1) The combustion gas flows downwardly through the narrow flow path of the exhaust port 30 flows laterally at a substantially right angle with the flow velocity G as described above, via the flue 33 communicated to the exhaust port 30; and furthermore flows upward at substantially right angles outside the external drum 21, thereby generating an extremely large air exhaust resistance. This air exhaust resistance prevents the combustion gas from smoothly flowing, and the expected effect can not be achieved, which is a problem to be solved.
(2) If cross-sectional areas of the exhaust port 30 and the flue 33 are made larger to solve this problem by smoothly flowing the combustion gas overcoming the large exhaust resistance, disturbance comes in at a flow velocity of V (m/sec) from an exhaust port of the flue 33 as indicated by the arrow mark in FIG. 1. Furthermore, if the flow velocity V is less than the flow velocity G of the combustion gas (V&lt;G), normal combustion is maintained, but in case of V&gt;G, disturbance comes into the combustion chamber 29, which prevents normal combustion. When the combuster 12 is in operation, the draft power in the flue 33 is generally expressed by the equation of Df.varies.H.times.(Tgm-To) (wherein Df is draft power, H is height, Tgm is an average temperature in the flue 33, and To is a temperature of peripheral air). Where the flue 33 has a large cross-sectional area, the quantity of heat radiated from the surface of the flue increases and the draft power is decreased, causing a load effect on combustion. When combustion is stopped, external air comes in from an opened exit of the flue 33 having a large cross-sectional area, which cools a heat insulation gas residing in the apparatus and generates convection therein. Then the heat insulation gas is exhausted via the flue 33 to outside and the temperature decreases. In such a system as an automatic hot water supply system, the combustor 9 operates to restart unnecessary heating, which results in wasted of energy and an increase in the operating cost. In addition, combustion state in the apparatus becomes unstable to interrupt combustion in the combustor 32 or generate oscillating combustion as well as to generated noises, which is another problem to be solved.